Process for machining in situ the peripheral surface of a rotating part, and apparatus for carrying out said process

Abstract

Process for machining in situ the peripheral surface (1100) of a rotating part, rotating around an xx′ axis (1), wherein a machining device is used comprising at least one plate (12) fixed to a frame and a tool holder (11) provided with a cutting tool (300), and mounted on the said plate such that it can move along a YY′ direction (3) substantially perpendicular to the xx′ axis of rotation (1). The tool holder is installed on the plate (12) such that it can pivot around an axis oriented along a ZZ′ direction (4) substantially perpendicular to the YY′ direction and to the xx′ axis of rotation. By combining a rotation of the tool holder around the XX′ axis and a translation of the centre (C) of rotation around the ZZ′ axis along the in-feed direction YY′, a displacement is imposed on the active end of the cutting tool (300) in a plane perpendicular to the ZZ′ axis. The device may also move along the third XX′ axis.

Description

DOMAIN OF THE INVENTION [0001] The invention relates to machining of rotating parts on site (on a machine and in the factory), and particularly to the renovation of commutators fixed to the armature or the rotor respectively of electrical motors, and that we will subsequently call “rotating contacts”. BACKGROUND OF THE INVENTION [0002] The invention was developed more particularly in order to renovate the surfaces of commutators or slip-rings that have peripheral circularity defects resulting from the friction of the brushes that maintain a sliding electrical contact with them. It is observed that these rotating contacts do no longer have a uniform radius around their entire periphery after the motor has been in operation for some time. To prolong the life of rotating contacts, limit brush wear and eliminate mechanical vibrations, a repair is made by abrasion resurfacing, typically “by stone” or grinding wheel, or by machining of the degraded surface. [0003] This type of repair is u...

AI Technical Summary

Benefits of technology

[0015] Preferably, the displacement along the in-feed direction YY′ of the centre of rotation around ZZ′ and the rotation of the tool holder around the ZZ′ axis, are motor driven, for example using a motor, moving the tool holder along the first slide (YY′ direction) through a screw—nut type assembly, and a motor rotating the tool holder around the ZZ′ axis. These motor driven movements may be controlled using a computer program such that the required trajectory is obtained by combination of the said movements. Furthermore, these movements can be slaved to improve machining parameters while cutting.

[0020] Since the surface to be machined may be long, it is advantageous if the plate is fixed to a base fixed onto the said frame, rather than fixed directly on a fixed point of the frame. The base itself is provided with a second slide running along the XX′ direction substantially parallel to the axis of rotation xx′ of the rotating part and the plate is provided with a second traveller, which has a section with a shape complementary to the shape of the second slide. The plate is thus mounted on the base such that it can move along the XX′ direction of the second slide. As a result, a plane displacement may be imposed on the active end of the cutting tool by combining a rotation of the tool holder around the ZZ′ axis with a translation of the centre of rotation around ZZ′ along the in-feed direction YY′ and a translation of the plate in the straight turning direction XX′.

[0022] As we have already seen, slaving of the YY′ axis also makes it possible to compensate for parallelism faults between the centre line of the commutator xx′ and the XX′ straight turning direction. However, this correction can only be limited and as the straight turning length increases, the need for good alignment between the xx′ and XX′ axes becomes more important. Typically, for a length of the surface to be resurfaced of the order of 600 mm, it is preferable to aim at the smallest possible angle between xx′ and XX′, typically less than 1°.

[0038] Preferably, the plate is not fixed directly on a fixed point of the frame, but onto a base fixed onto the said frame. The base itself is provided with a second slide running along the XX′ direction substantially parallel to the axis of rotation xx′ of the rotating part, and the plate is provided with a second traveller, which has a section with a shape complementary to the shape of the second slide. The plate is thus mounted on the base such that it can move along the XX′ direction of the second slide. The base may be in one or several parts, provided that the second slide moves along this perfectly straight direction and can move the plate smoothly.

Problems solved by technology

It is observed that these rotating contacts do no longer have a uniform radius around their entire periphery after the motor has been in operation for some time.

This type of repair is usually an expensive operation that immobilises the motor for a long period.

This has several disadvantages; firstly, a stock of spare motors has to be provided that will be used for the repair time of the disassembled motors; and secondly, reassembly requires special care to achieve difficult realignment of the commutator / armature axis or ring / rotor axis.

However, the presence of these walls at one end and / or at both ends of the commutator makes it impossible to use a single tool to machine the entire surface of the commutator over its entire useful length, due to the size of parts used to hold the cutting tool.

Moreover, the ends often have to be chamfered.

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